Enable building on bionic

[jspiewak]

Tweak comments, brackets, etc.

[colearendt]

Latest failed on the animation package:

/tmp/RtmpB4Ft8P/downloaded_packages/animation_2.6.tar.gz
files: /tmp/RtmpB4Ft8P/downloaded_packages/magick_2.0.tar.gz, 
	/tmp/RtmpB4Ft8P/downloaded_packages/animation_2.6.tar.gz
* installing *source* package ‘magick’ ...
** package ‘magick’ successfully unpacked and MD5 sums checked
Package Magick++ was not found in the pkg-config search path.
Perhaps you should add the directory containing `Magick++.pc'
to the PKG_CONFIG_PATH environment variable
No package 'Magick++' found
Using PKG_CFLAGS=
Using PKG_LIBS=-lMagick++-6.Q16
------------------------- ANTICONF ERROR ---------------------------
Configuration failed because Magick++ was not found. Try installing:
 - deb: 'libmagick++-dev' (Debian, Ubuntu)
 - rpm: 'ImageMagick-c++-devel' (Fedora, CentOS, RHEL)
 - csw: 'imagemagick_dev' (Solaris)
On MacOS it is recommended to use install ImageMagick-6 from homebrew
with extra support for fontconfig and rsvg rendering:
   brew reinstall imagemagick@6 --with-fontconfig --with-librsvg
For older Ubuntu versions Trusty (14.04) and Xenial (16.04) use our PPA:
   sudo add-apt-repository -y ppa:opencpu/imagemagick
   sudo apt-get update
   sudo apt-get install -y libmagick++-dev
If Magick++ is already installed, check that 'pkg-config' is in your
PATH and PKG_CONFIG_PATH contains a Magick++.pc file. If pkg-config
is unavailable you can set INCLUDE_DIR and LIB_DIR manually via:
R CMD INSTALL --configure-vars='INCLUDE_DIR=... LIB_DIR=...'
--------------------------------------------------------------------
ERROR: configuration failed for package ‘magick’
* removing ‘/opt/R/3.5.3/lib/R/library/magick’
ERROR: dependency ‘magick’ is not available for package ‘animation’
* removing ‘/opt/R/3.5.3/lib/R/library/animation’

[stevenolen]

focal is the current base, don't think we need this any more!